We will continue to study the pathology of congenital heart disease on a city-wide basis. At the gross level this includes correlation with echocardiography, and angiocardiography, and the description of the complexes not yet studied which will be useful for the surgeon. At the histologic level this includes the study of the myocardium, endocardium and valves in various complexes, and especially the study of these structures in patients who live long after surgery. We will make a statistical analysis and computerize the more than 5,000 congenital hearts we have accumulated in the last 24 years. This will form the basis of a book on congenital heart disease. As concerns the conduction system, we will study hearts with all types of congenital and acquired heart block, preexcitation, (WPW) in normally formed and congenital hearts, supraventricular, ventricular arrhythmias and hearts from patients with sudden death in all age groups. This includes a study of the nerves of the conduction system in all these abnormalities. The course of the conduction system in surgically important congenital heart defects not yet described will be depicted. In all these studies, emphasis will be placed on electrophysiologic (His bundle) and electrocardiographic correlation. The methodology to be used is (1) the study of congenitally abnormal hearts qualitatively and quantitatively according to methods originally described by Lev and modified by Bharati and Lev. (2) The study of the conduction system as originally described by Lev and modified recently by Lev and Bharati. The long term objectives are, (1) to help the surgeon and clinician in the treatment of congenital heart disease by giving him sound qualitative and quantitative anatomic data, (2) to study the patient after long survival after surgery on congenital heart disease, who dies suddenly, or who lives out his expected life time. This is a new flora of patients with new types of pathology we have never seen before, (3) to give an anatomic base to conduction disturbances so that they may be treated better clinically and surgically.